The present invention relates to an anvil positioning device with an interchangeable anvil for riveting operations performed by automatic machine tools.
In particular, it relates to a positioning device, designed to be fitted to a support with several degrees of freedom, which positions the anvil spatially.
The present invention relates to the field of automatic machine tools, and in particular to automatic machine tools which are used to assemble aircraft parts, e.g., to fit the skin of the aircraft onto the load-bearing structure of the aircraft. The difficulties encountered in performing these operations correctly and within the manufacturers' tolerances are well known.
Various tools are need to be brought to the the rivets which are positioned at right angles to the surface, whatever its inclination, and automatically perform the various operations required, such as drilling, flaring, adhesive spreading, rivet insertion, rivet driving, etc., while keeping within narrow positioning and orthogonality tolerances.
The equipment which is able perform these operations on various types of structures is already known; in particular, one such type of equipment is described in U.S. Pat. No. 5,004,064 held by the Applicant.
This reference relates to a machine tool comprising a support which moves along three cartesian axes, an operating head with two degrees of freedom fitted to the said support, and a plate with connection points for a positioning device, the plate is fitted to the operating head and able to perform controlled movements along a pair of cartesian axes.
These machines however, present some problems in the case where rivet insertion into the structures of rather complex shape, such as those shown in FIGS. 1a, 1b, 1c, 1d and to 1e which schematically illustrate some possible configurations of the internal ribbing of the structure to be assembled, each of which calls for a different anvil.
Normally, the hammer of the anvil which drives in the rivet works on the outside of the structure (i.e. on the side of the panel to be attached to ribbing or the like), while the anvil is placed against the rivet on the inside. The anvil, therefore needs to be inserted into structures of quite complex shape while always remaining perpendicular to the surface, and the anvil axis must pass through the rivet.
It is therefore necessary to replace the anvil whenever operations change over from one structure to another, so that the right tool can always be used.
Another problem is posed by the need to position the anvil at an angle around its own axis as operations move along the structure to be assembled which, as already mentioned, is generally curved in both directions and has ribs of various shapes.
This characteristic makes it difficult, if not practically impossible, to design a single anvil suitable for all jobs (or all of the different types of area to be worked on) which possesses the correct attributes of pressure bar, rivet crushing, robustness and ease of manufacture.